'Transparent colours painted on glass, either in water or varnish, can never attain the brilliancy of the coloured glass; but from the great difficulty of staining certain colours, it is very common to find, in modern windows, part of the colours painted on the surface, whilst the large tints are stained.
It was not until the 15th century that the stained glass was made to produce the effect of strong lights and shades; but respecting the methods employed by the painters of those superb specimens which we find in cathedrals, we arc wholly uninformed ; and our information is now chiefly drawn from a ;Memoir of M. Leviel, published in the De scription des .9rts et Metiers, vol. xiii. This gentleman was himself a painter on glass, and the only one of emi nence who has written upon the art.
The glass upon which it is intended to paint should be very hard, without spots, or any colour. Crown window glass is the best ; for cast or plate glass has borax in its composition, which would make the colours to run or spread. When the design is too large to be contained on a single piece of glass, several mustbe fitted to one another, and a bed of some resinous cement prepared, upon which they can be readily put together, and held on one flat sur face whilst painted, with proper spaces for the lead frames, and yet be readily separated, to subject the pieces separate ly to the fire.
In arranging the pieces of glass which are to be painted, care must be taken to dispose the joints so that they may do the least injury to the design by the opacity of the lead frames, by which the pieces must be joined together, in or der to form a large window.
The design which is intended to be painted upon the glass, must be accurately drawn upon a sheet of paper in outline; or, if necessary, in its proper colours. In this species of painting, the artist works quite in the dark as to the effect of his picture, because the colours are produced by the fire ; and when the preparations are laid on the glass, they are either colourless, or perhaps have colours quite different from that with which they will ultimately stain the glass.
The design drawn upon the paper, is placed beneath the plate of glass, or upon the bed, when several separate pieces are used. The upper side of the glass is then brushed or sponged over with a fine clear gum-water. This, when pet fectly dry, forms a surface proper to receive the colours, without danger of their running or spreading beyond their intended limits, as they would do if laid upon the smooth surface of the glass. The first operation is, to
draw upon the glass, with a fine pencil, all the lines which are necessary to produce the shades, and to mark the out lines. This is usually done in a black colour, or at least in some deep colours, such as brown, blue, or green, and sometimes red. In laying on these, the artist is guided by the same principles as the engraver, when he produces the effect of light and shade, by dots, lines, or hatches; and he employs that colour to produce the shades, which will best accord with the colour which is intended afterwards to be laid on ; but, in general, black is used in the outline for all the deeper shades. When this is finished, the whole pic ture will appear represented in lines or hatches similar to an engraving, finished up to the highest effect possible ; and afterwards, when it is pet fectly dry, the colours are laid on by means of larger pencils. Earli colour is upon tile part of the design which remiires it ; as the lksh colour upon the faces of the figures, the green blue for the sky, b c ; but in doing this, the artist ktbom s of being unable to see the effect of his work, until it has been subjected to the lire. lit thvro foic avails himself of a number of trials made upon pieces of glass, which he keeps as specimens of the efief:t of the different colours, properly numbered, to cotrespoi,d with the preparations which he employs for colcui ing : lac must, therefore, search among these specimens for the tint, and apply the proper preparation.
In laying on the cblours, it must be observed, that some preparations which produce beautiful colours, are liable to run or mix with those which are adjacent to them, so as to confound the outlines of each respective colour, by pro ducing a mixture of the two, This is a serious difficulty ; the artist must refer himself to his trials ; and when he finds it necessary to lay two adjoining colours, which will run together, he must lay one of them on the back of the glass. The few principal colours, of which we shall presently give the preparation, arc all fast colours, such as will riot run, except the yellow, which must therefore be laid upon the opposite side. It should be observed, that those colours which will mix or run, are equally useful with the others when applied to produce compound tints ; but the artist should not attempt to use them without being well ac quainted with their properties, otherwise he may by a very small tint of improper colour destroy all his work.